Sun Yat-sen University study finds sputtering patterns “turn”

Recently, the team of Xiao Zhiyong, a professor at the School of Atmospheric Sciences of Sun Yat-sen University, found that non-radial sputtering patterns on the surface of celestial bodies will “turn”. The study was published in Nature Communications.

On the surface of Solar System bodies, the most common geomorphological feature is impact craters formed by asteroid and comet impacts. The celestial impact is accompanied by a huge release of energy, similar to a missile or buried nuclear explosion, but the impact creates a “crater” that can be thousands of kilometers in diameter and ejects a large amount of sputtered material outward. Among them, the most dazzling are the bright sputter patterns, some of which can cover the whole world. Sputters are generally thought to be distributed radially around the central crater.


False-color image of Mercury (4880 km diameter) with bright white bands of sputtering patterns formed by impact craters. Photo courtesy of the research team

“We found that sputter patterns ‘turn’.” Xiao Zhiyong, the corresponding author of the paper, explained the sputtering pattern of the “turn”. He said non-radial sputtering patterns are prevalent on the surfaces of Mercury, the moon and Mars. The phenomenon of bending of sputtering patterns is an inherent product of the impact process.

Why do sputter lines bend? Xiao explained that the trajectory of ballistics on rotating celestial bodies is affected by the rotation of celestial bodies (i.e., the Coriolis force effect), so sputtering patterns may bend. Taking Mercury as an example, if it is a rotation period of almost 6 Earth days, the deposition pattern can have a clear “turn” phenomenon after the impact sputter undergoes a ballistic flight over Mercury. This possibility is interesting because there is still controversy over hot research questions such as when Mercury reaches tidal lock and when Mercury’s lithospheric structure forms, and these problems are closely related to Mercury’s rotation speed.

“In addition to the effects of celestial rotation, the heterogeneity of the impact process is sufficient to explain these anomalous sputter distributions.” Xiao Zhiyong said. The team’s research through particle swarm ballistic flight simulation found that this curved sputter pattern on Mercury is not caused by faster rotation speed, but by a sudden sputtering angle. There is extensive heterogeneity in the impactor and the target before impact, with different impact impedances, which in turn affects the propagation and interaction mode of shock wave and sparse wave, and finally causes sudden changes in sputtering angle.

The study found that it erects a guardrail for the reliability of the widely used Steno’s Law: the overlapping relationship of geological units is the basis for determining the relative relationship between new and old surface materials of extraterrestrial objects, and it is also the basic law for constructing global and regional stratigraphic systems; However, the mutation of the sputtering angle may cause sputters from the same crater to be deposited in the same location from different directions at different points in time, forming pseudotangent relationships.

Xu Rui, the first author of the paper and a doctoral candidate at the School of Atmospheric Sciences of Sun Yat-sen University, pointed out that the study also proposes technical improvements to the widely used dating method based on impact crater statistics: the sputtering angle mutation forms many background secondary craters that are not easy to identify and exclude, and the statistical dating of impact craters requires cross-regional comparison. (Source: China Science News Zhu Hanbin)

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